Electroluminescent display device having etched character electrodes

ABSTRACT

An electroluminescent display device is provided, in which a substrate of the display is comprised of character electrodes, external connecting means for facilitating connections to external apparatus and a plurality of interconnecting means between the character electrodes and external connecting means. The character electrodes, interconnecting means and external connecting means form one integral unit, with the display device itself being a monolithic structure.

XX 9 m UN 3 Gerald Boucher Hudson, NH. 731,191 May 22, 1968 PatentedApr. 6, 1971 Sanders Associates, Inc. Nashua, NH.

HAVING ETCHED CHARACTER ELECTRODES 4 Claims, 3 Drawing Figs.

Appl. No. [22] Filed 1 Assignee Inventor United States Patent [54]ELECTROLUMINESCENT DISPLAY DEVICE An electroluminescent device is pro-Holk l/6O vided, in which a substrate of the display is comprised ofField of hara ter electrode external onnecting means for facilitat. 108;315/169 (TX), 169; 317/234 (27); 40/13 ing connections to externalapparatus and a plurality of inter- (M); 136/86 connecting means betweenthe character el ectrodes and external connecting means. The characterelectrodes, interconnecting means and external connecting means form oneinelf being a monolithic tegral unit, with the display device itsstructure.

References Cited UNITED STATES PATENTS 11/1966 Dickson et al.

ELECTROLIUMIINESCENT DIISEEAY DEVICE IHIAVIING ETCI-IIER CHARACTERELECTRODES FIELD OF THE INVENTION This invention relates to a means forproviding a visual display in which any of many predetermined displaypatterns, such as letters, numbers, graphs or symbols can be selectivelyilluminated, and more particularly, to such displays in which anelectroluminescent phosphor layer disposed between two electrode layers,a transparent electrode and a preformed character electrode, is excitedby an electric field causing the associated phosphor area to luminescethereby illuminating the selected character.

THE PRIOR ART In the field of electroluminescent display assemblies, itis conventional practice to make the exterior glass or other transparentmaterial the substrate of the display. Such substrates, while rigid,provide a display that is heavy and relatively fragile. ln completingthe structure of these conventional displays, a tin oxide coating or anyother light-transmitting electrically conductive material is applied toone surface of the glass plate thus forming the transparent electrode.An electroluminescent phosphor layer which may be comprised of adielectric material such as glass or plastic having dispersed thereinparticles of an electric field responsive phosphor is placed adjacentthe transparent electrode. The dielectric material and the phosphor canbe applied as separate layers. A metallic configuration electrode orcharacter electrode composed of steel, aluminum, gold, copper, or otherelectrically conducting material is bonded to the electroluminescentphosphor layer. The metallic configuration electrode may be used as thebacking surface of the display or a layer of dielectric material may belaminated to the electrode surface.

In the operation of devices such as described above, an electricalpotential is applied between the metallic configuration electrode andthe transparent electrode creating an electric field across the phosphorlayer, thus, producing visible light which identifies the characters tobe displayed. In order to apply this power, electrical connections mustbe made to the transparent electrode and the character electrode(s).

This requirement necessitates that electrical connections be made tovery thin metallic electrodes. From a manufacturing viewpoint, the taskof making relatively fragile electrical connections coupled with therelative weakness of the electroluminescent displays, because a glasssurface is used as the substrate, presents many problems.

The solution to the problem of providing solid electrical connections tothe character electrodes lies in forming a substrate in which thecharacter electrodes and interconnecting means are an integral partthereof. In providing such a substrate, the relative weakness of thedisplay is also eliminated because the outer glass surface no longerfulfills this function.

SUMMARY OF THE INVENTION From the foregoing, it will be understood thatamong the objects of this invention are the following:

to provide an electroluminescent display in which the characterelectrode pattern, the insulating material, and the interconnectingconductive members provide a rugged substrate for the phosphor layer andthe transparent electrode;

to provide an electroluminescent display which is light in weight,compact, rugged and more reliable than heretofore available;

to provide an electroluminescent display in which the use of solderedjoints or conductive cement between the electrode segments and theelectrical connection leads are eliminated;

to provide an electroluminescent display in which the bonding of theindividual electrode areas to the electroluminescent phosphor layer iseliminated;

to provide an electroluminescent display that is relatively free ofproduction problems and is inexpensive to manufacture;

to provide an electroluminescent display in which the electrodepatterns, the transparent electrode, the electroluminescent phosphorlayer, and the interconnecting conductive members to the externalelectronic circuits form a monolithic structure.

In accordance with this invention, these objectives are achieved byforming the character electrodes and electrical interconnecting circuitsthereto as an integral component of the substrate of theelectroluminescent display. That is, the character electrodes, theelectrical circuit paths within the substrate and the conductive memberswhich extend through the insulative material that surrounds andseparates the character electrodes and the circuit paths are molecularlyunited without the necessity of soldering or the like when formed by aprinted circuit process, and form an integral unit. In this manner, thepassive elements of the display are formed as part of the substratewhich supports the active elements of the display and thereby provide adurable, rugged display.

For a clearer understanding of the nature and objects of my invention,reference may be had to the following detailed description taken inconnection with the accompanying drawings, in which:

DESCRIPTION OF THE DRAWINGS FIG. I is a schematic view of various typesof character electrodes;

FIG. 2 is a partial perspective view of the character electrodes, andtheir associated printed circuit interconnecting means, and

FIG. 3 is a cross-sectional view of a complete electroluminescentdisplay.

It will be understood that these FIGS. present an enlarged view of theelectroluminescent display for clarity and illustration purposes only.The dimensions of a finished display are greatly reduced in surface areaand depth. Also, the number of character electrodes, the number ofconductive members between circuit levels, and the number of associatedelectrical interconnecting circuit paths and terminals have been limitedfor illustration purposes only.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. ll, thereis. shown an electroluminescent display having various types ofpreformed permanent character electrodes 112 (a-e) comprising varioussymbols, designs, etc.

It is apparent from an examination of the characters 112 (a- -e) thatthe actual character configuration which can be formed is unlimited. Anyshape or pattern may be produced by a printed circuit process therebyproviding numerous applications for this display. For example, theelectrode segments may be formed into a circular pattern 12a whereby theradial segments can represent, for example, a metal dial or the hands ofa clock. The character electrode ll2b represents a letter of thealphabet. A seven segment presentation is illustrated by 12c such thatany illuminated number from zero to nine may be produced by energizingthe proper segments. A l4-segment presentation 124, can with properenergization of the seg ments, provide any number of letter of thealphabet. Likewise, a 7-segment or fraction presentation He is employedto provide illuminated numerical digits whether as a fraction or as avalue in tenths. These configurations are shown by way of example only.In addition, substrate III, as will be subsequently explained, includesconnection means 113 to connect the permanent character electrodes 12(a-e) to external apparatus. Connection means 13 may consist of eyelets,protruding pins or other known methods or combinations thereof toprovide an electrical connection for external apparatus.

Referring now to FIG. 2, there is shown a partial electroluminescentdisplay (substrate 1111) showing the character electrodes, associatedprinted circuits, and interconnecting means.

The method of construction of substrate 11 may vary as to the initialsteps depending upon the type of connection means 13 used to facilitateconnections to external apparatus. In any event, the methods by whichconnection means I3 are incorporated as part of substrate 11 are wellknown in the art.

The formation of the substrate 11 starts with a sheet of copper (to beformed into pillars or lands I4 and circuit paths 16) that is preferablythick enough such that operations may be performed on it without theneed of a supporting device.

The copper sheet is thoroughly cleaned, coated with a light sensitiveresist, dried and covered with a film mask which locates the upstandingconductive members or lands 14. The copper layer is then exposed tolight (preferably ultraviolet), developed, rinsed, dried, dyed ifdesired, dried and touched up, and etched to a predetermined controlleddepth to form the desired upstanding portions or lands. The surface isthen flushed, dried and the exposed resist removed. It is then againrinsed and dried. A layer of epoxy fiber glass I or other insulatingmaterial is laminated over and surrounding the upstanding conductivemembers or lands 14. The surface of the insulating material is thensanded, ground, or otherwise thinned down to remove the excess epoxy toleave the uppermost surface of the lands l4 exposed and cleaned. Thismethod for providing lands I4 is similar to that set forth with moreparticularity in my U.S. Pat. No. 3,374,l29, assigned to the assignee ofthis application. The surfaces of the lands 14 will be molecularlyunited to the character electrodes I2 of FIGS. 1 and 2.

The opposing surface of the sheet of copper I0 is resist coated, washed,exposed to light, developed, rinsed, dried, dyed if desired, dried andtouched up, and etched to form an appropriate printed circuit layer 16.This surface is then cleaned and a layer of epoxy fiber glass 17 orother insulating material is laminated thereover.

The surface of the laminate with the exposed conducting members or lands14 is then cleaned, and activated by being dipped in hydrocloric acid,dipped in a suitable catalyst, rinsed, dipped in a copper mix solution,dipped in fluoboric acid, electroplated with copper to form a layer,rinsed and dried. The copper layer which will be formed into thecharacter electrodes '12, is then cleaned, coated with a light sensitiveresist, dried and covered with a film mask to locate the permanentelectrode characters. This copper layer is then exposed to light,developed, rinsed, dried, dyed if desired, dried and touched up, andetched to form the desired patterns which are the second or permanentelectrode characters. such as electrode segment [2e illustrated in FIG.2.

Note that since the character electrodes 12 are made by a printedcircuit process, the electrodes may be formed into any form imaginableand, therefore, the use of the display is almost without limit.

The electrode segments 12 (a-e) in this embodiment are located withinthe same plane and, therefore, spacing therebetween is selected tominimize any tendency for an electrical breakdown. To insure against anelectrical breakdown between the electrode segments, a layer ofinsulative material may be placed around and over the electrodes and thesurface then ground, sanded or otherwise thinned down to expose theuppermost surface of the electrode segments 12. A base is therebyprovided to which is applied a uniform layer of phosphor material (notshown in FIG. 2). A uniform layer of phosphor material ensures that eachcharacter is illuminated with the same degree of brightness.

By utilizing the method, herein described, for producing theinterconnecting printed circuits 16 it is possible that each characterelectrode I2 may have a multiple of interconnection contacts. Forexample, segment (a) of the character electrode 12c, FIG. 2, may beintegrally connected by a multiple of printed circuit leads l8 and 19 tomore than one external connecting means 13. Although not illustrated,the printed circuit leads may be interconnected between segments ofvarious character electrodes. For example, if the display was to presentcertain combinations of letters or numbers then the letters could beinterconnected such that only one circuit path needs to be connected toonly one external connecting means 13. In this manner, the samecharacter electrode may be shared by more than one external systemthereby increasing its usefulness. The connecting means 13 may beeyelets which extend through the electroluminescent panel, illustratedas 13b, FIG. 2 or the connecting means 13 may be eyelets which onlyappear on one side of the electroluminescent panel such as 13a, FIG. 2.In any event, the method of inserting these eyelets is well known.

The above-described construction is very rugged, durable, and capable ofwithstanding excessive external forces without any danger ofinterrupting the electrical circuits between the connection means 13 andthe character electrodes 12. There is little danger that one of thecharacter electrodes 12 be separate from a phosphor layer which has beenapplied to the electrodes. Thus, the electroluminescent displaydescribed herein attains the goals set forth in the objects of theinventIOI'l.

The embodiment of the invention described herein has one circuit layer16 beneath the permanent character electrode 12. This concept, however,is not limited to any particular number of printed circuit levels, foras many levels may be formed as deemed necessary by following the stepsoutlined above.

Although the electrical connection means 13 for the electroluminescentdisplay are illustrated as surrounding the electrode segment (see 12a ofFIG. I) or positioned along the perimeter of the display device (seel2b-l2e, FIG. 1), their placement is not restricted to these twolocations, but will depend on the associated interconnecting leads tothe electrical apparatus. Also, the connection means 13 is notrestricted to protruding pins or eyelet types, but for example, may bein the shape of an exposed tab or any other known means. The connectionmeans 13, however, do not extend through or come in contact with thedielectric layer 21, phosphor layer 22, transparent electrode 23, or thecover coating 25 (see FIG. 3). If the connection means 13 should come incontact with the transparent electrode 23 in particular, then a directelectrical circuit would exist between the transparent electrode 23 andthe character electrodes 12 and the phosphor layer would not luminesce.

Referring now to FIG. 3, there is illustrated a complete structure of anelectroluminescent display device 20. A dielectric breakdown layer 21 ofbarium titanate intermixed with a dielectric resin binder is appliedover the layer of character electrodes I2. Adjacent to and above thedielectric breakdown layer 21, a phosphor layer 22 is applied by anysuitable process, such by spraying, silk screening or other knownmethods. The phosphor layer 22 comprises any electroluminescent phosphormaterial in which the phosphors are energizablc by electric fields toproduce visible light, and accordingly are termed field responsive." Asa specific example, the electroluminescent material may comprise zincsulfide activated by copper and coactivated by chlorine, but any othersuitable electroluminescent material may be substituted therefor. Thephosphor may also be intermixed with a suitable light-transmittingdielectric material.

Adjacent to the phosphor layer is the first electrode 23. The firstelectrode 23 consists of a thin, light-transmitting, electricallyconducting material which is coated as a thin film on a fibrous glasssheet or other vitreous body by, for example, iridizing. An example ofsuitable materials employed are tin oxide, stannic oxide, or indiumoxide. The transparent electrically conductive layer 23 usually is onesheet covering all of the character electrodes I2 but, if necessary, itmay be applied in sections such as to cover each character electrodeindividually. A conductive lead 24, FIG. 3, is bonded to thelight-permeable, electrically conductive electrode. This lead is madeavailable for connection to an external power source through aconnection means (not shown), for example, a tab may be soldered theretoand brought out from the body of the display. A voltage potential,applied between the transparent electrode and any one characterelectrode 112, causes the as sociated phosphor material to luminesce,thereby illuminating the display 20. The connection to the characterelectrode R2 is made at a connection means t3 (not illustrated in thisFIG.) as shown in H0. 2. Where it is necessary to protect the panel fromthe effects of the atmosphere such as moisture or dust, the transparentelectrode 23 and surrounding areas, if any, may be covered with a layer25 of transparent plastic glass or other suitable bondable material.

While the instant display device is not limited in the size in which itcan be fabricated, it is particularly adapted for small displays. Thecompactness of the display has as its practical limitation the observersability to visually perceive and distinguish the characters of thedisplay, while the largeness of the display area is guided by practicalconsiderations. Another advantage of my invention is the wafer-thinthickness of the display. This thinness makes the display deviceparticularly adaptable for use in areas where relatively bulky displayspresent design packaging problems.

The operation of the electroluminescent displays is carried outaccording to methods known in the art; that is, any one of the characterelectrodes 12 or combination of character electrodes 112 may beenergized to illuminate the electroluminescent display device 20. Thisis done by applying a volt age potential between the transparentelectrode 23 at conductive lead M, and any one or combination ofcharacter electrodes l2.

It will be appreciated from the foregoing description that theelectroluminescent display of this invention has efficiently attainedthe objectives previously set forth. That is, the external connectionmeans 113, the circuit layer 116, the upstanding conductive members orlands M, and the character electrode segments 112 are molecularly unitedso as to form one integral electrical circuit; and this integralstructure combined with the insulative material which is formed aroundthe electrical elements and is flush with the uppermost surface of thecharacter electrodes llZ provides a very durable, rugged substrate forthe display that is not present when a piece of transparent glass isused as the substrate. In addition, a display device produced by thismethod is wafer-thin in size and light in weight permitting usage wherethese factors are important. Also, it is apparent that my inventionprovides a simplified and economical construction of a monolithicelectroluminescent display.

This invention has been described in conjunction with preformedcharacters which display numbers, letters, or simple designs. But, it isseen that by extending the concept of using multiple interconnectingprinted circuit paths, one can develop a system which when used with anappropriate electronic coding circuits will produce phrases, words,animated cartoons, or moving displays. Thus, the potential applicationsof this type of display are unlimited Thus, while the abovedescriptionrelates to specific principles of this invention, it is to be understoodthat this description is made only by way of example and not as alimitation thereon, for one skilled in the art may make modificationthereto, but still be within the true spirit and scope of this inventionas set forth in the appended claims.

lclaim:

ll. An electroluminescent character display device compris .ing:

a substrate subassembly including first and second etched circuits, saidsecond etched circuit formed in the shape of desired characters, a layerinsulating said circuits, and at least one solid electrically conductivemember extending through said insulating layer, being integrally formedwith and molecularly united to said first and second circuits such as tohave a homogeneous grain structure therewith;

a transparent layer of electrically conductive material;

a layer of field responsive electroluminescent phosphor materialdisposed between said second etched circuit and said transparent layerof electrically conductive material; and

an electrical insulating layer disposed upon said transparent layer ofelcctrically conductive material.

2. Apparatus as recited in claim 1 further including:

at least one electrically conductive member molecularly united to andhaving a homogeneous grain structure with said first etched circuit andtraversing said insulating layer to an exterior surface thereof.

3. Apparatus as recited in claim ll further including:

a layer of dielectric material disposed between said second etchedcircuit and said field. responsive electroluminescent phosphor layer.

4. Apparatus as recited in claim 1 further including:

a layer of transparent insulating material bonded to the surface of saidtransparent electrically conductive layer opposite said phosphor layer.

1. An electroluminescent character display device comprising: asubstrate subassembly including first and second etched circuits, saidsecond etched circuit formed in the shape of desired characters, a layerinsulating said circuits, and at least one solid electrically conductivemember extending through said insulating layer, being integrally formedwith and molecularly united to said first and second circuits such as tohave a homogeneous grain structure therewith; a transparent layer ofelectrically conductive material; a layer of field responsiveelectroluminescent phosphor material disposed between said second etchedcircuit and said transparent layer of electrically conductive material;and an electrical insulating layer disposed upon said transparent layerof electrically conductive material.
 2. Apparatus as recited in claim 1further including: at least one electrically conductive membermolecularly united to and having a homogeneous grain structure with saidfirst etched circuit and traversing said insulating layer to an exteriorsurface thereof.
 3. Apparatus as recited in claim 1 further including: alayer of dielectric material disposed between said second etched circuitand said field responsive electroluminescent phosphor layer. 4.Apparatus as recited in claim 1 further including: a layer oftransparent insulating material bonded to the surface of saidtransparent electrically conductive layer opposite said phosphor layer.